Issue 38, 2021

Scaffold-based [Fe]-hydrogenase model: H2 activation initiates Fe(0)-hydride extrusion and non-biomimetic hydride transfer

Abstract

We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor. In comparison to other non-scaffolded acyl-containing complexes, the complex described herein retains molecularly well-defined chemistry upon addition of multiple equivalents of exogenous base. Clean deprotonation of the acyl(methylene) C–H bond with a phenolate base results in the formation of a dimeric motif that contains a new Fe–C(methine) bond resulting from coordination of the deprotonated methylene unit to an adjacent iron center. This effective second carbanion in the ligand framework was demonstrated to drive heterolytic H2 activation across the Fe(II) center. However, this process results in reductive elimination and liberation of the ligand to extrude a lower-valent Fe–carbonyl complex. Through a series of isotopic labelling experiments, structural characterization (XRD, XAS), and spectroscopic characterization (IR, NMR, EXAFS), a mechanistic pathway is presented for H2/hydride-induced loss of the organometallic acyl unit (i.e. pyCH2–C[double bond, length as m-dash]O → pyCH3+C[triple bond, length as m-dash]O). The known reduced hydride species [HFe(CO)4] and [HFe3(CO)11] have been observed as products by 1H/2H NMR and IR spectroscopies, as well as independent syntheses of PNP[HFe(CO)4]. The former species (i.e. [HFe(CO)4]) is deduced to be the actual hydride transfer agent in the hydride transfer reaction (nominally catalyzed by the title compound) to a biomimetic substrate ([TolIm](BArF) = fluorinated imidazolium as hydride acceptor). This work provides mechanistic insight into the reasons for lack of functional biomimetic behavior (hydride transfer) in acyl(methylene)pyridine based mimics of [Fe]-hydrogenase.

Graphical abstract: Scaffold-based [Fe]-hydrogenase model: H2 activation initiates Fe(0)-hydride extrusion and non-biomimetic hydride transfer

Supplementary files

Article information

Article type
Edge Article
Submitted
05 Jun 2020
Accepted
01 Sep 2021
First published
10 Sep 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2021,12, 12838-12846

Scaffold-based [Fe]-hydrogenase model: H2 activation initiates Fe(0)-hydride extrusion and non-biomimetic hydride transfer

S. A. Kerns, J. Seo, V. M. Lynch, J. Shearer, S. T. Goralski, E. R. Sullivan and M. J. Rose, Chem. Sci., 2021, 12, 12838 DOI: 10.1039/D0SC03154B

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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